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Slim chance

The first genetic mutation to be linked with anorexia has been revealed. A Dutch team has associated the disease with a mutation in a gene coding for a protein important in regulating food intake.

“People with the mutation may find it much easier to lose weight, because they don’t feel that hungry,” says researcher Roger Adan of Utrecht University.

The discovery will aid scientists’ understanding of the causes of anorexia, but it will help explain only a minority of cases, says Adan. His team found that the mutation is present in 4.5 per cent of people without anorexia, and in 11 per cent of 145 anorexic patients in the study.

Previous research on the incidence of anorexia in families has suggested that genes play a part. “It’s clear that in anorexia nervosa, there is a genetic component contributing to susceptibility. But there will not be a single gene involved,” Adan told New Scientist.

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Nonetheless, he adds&colon; “It is important that people realise anorexia is not only psychological, but that biological factors are also involved,”

Steve Bloomfield of the Eating Disorders Association based in Norwich, UK, says&colon; “This is interesting, but the causes of anorexia are very complicated. We need more research to understand the links between the basic eating aspects of the disease and the psychological aspects.”

Balancing act

The gene studied by Adan’s team produces the Agouti-related protein (AgrP). AgrP helps the body balance food intake with energy expended. Higher levels suppress the activity of certain receptors in the brain, called melanocortin receptors, and this stimulates hunger.

Earlier work has associated over-suppression of the receptors with obesity. The new study suggests that in some patients with anorexia nervosa, there may be under-suppression of the same receptors.

“From a biological standpoint, you could say that anorexia nervosa is the opposite of obesity,” says Adan. “The same receptor could be involved in eating too much or eating too little.”

Work on obesity drugs that inhibit suppression of the receptors is ongoing. It may be possible to develop drugs that do the reverse to help treat anorexia in patients with the gene mutation, he says.

But Adan agrees that genetic factors alone are not to blame. Last year, the British Medical Association identified a link between images of “abnormally thin” models in the media, and an increase in cases of anorexia and bulimia nervosa.

The most common treatments for anorexia involve behavioural therapy – helping patients to modify their attitudes to food and eating. But these treatments are generally not very successful, Bloomfield says.